Check engine light -- 1997 850 GLT Wagon --how to turn it off?

You can read the code and turn off the light with any OBD-II compliant reader.

and turn off the light with any OBD-II compliant

I looked it up, and CarMD seems to be an OBDII compliant reader. It won't be the most convenient to use - you will have to look up in a book what the codes mean rather than them displaying on the readout - but it should do the job. The instructions will tell you how to "clear the codes" which will turn off the light... at least for now. Write the codes down before you clear them. They will be in the form of P----, like P0410.

There are three possible outcomes in this. First, the code may clear successfully and never come back or only come back sporadically. Second, the code may clear and come back in a few hours or days. Third, the code may come back immediately. When and if the code returns the "check engine" light will come on. If you post the codes we (especially the people here who know the 850 well) can tell you what is probably happening and what you can do about it.

Mike